1. Field of the Invention
The present invention relates to large-capacity high-speed signal transmission in an optical transport network (OTN), and more particularly, to a method and apparatus for increasing a transmission capacity for an embodiment of a large-capacity back plane in an OTN.
2. Description of the Related Art
Existing various networks support various types of signal frames, transmission speeds, or multiplexing methods that are different from each other. Although conventional networks used to be independently operated, forming various types of technology fields and markets for voice, image, and data transmission, demand for a service providing a united network has gradually increased.
Accordingly, research into various types of methods of making signals in the conventional networks compatible are being carried out.
The International Telecommunications Union—Telecommunication (ITU-T) Standardization Sector indicates that an Optical Transport Hierarchy (OTH), that is, a signal hierarchy in an optical transport network (OTN), specified in G.709 is based on a conventional Synchronous Digital Hierarchy (SDH) that was developed in regard to the OTN. The OTH provides a frame structure which can support various types of networks such as the SDH, an Asynchronous Transfer Mode (ATM), or a General Framing Procedure (GFP) as tributary signals.
Meanwhile, a Synchronous Optical Network (SONET) that is an American standard of the SDH is almost the same standard and has almost the same function as the SDH, and therefore these standards will be indicated as SDH for convenience.
In order to transmit data together with an image by using a conventional transmission method that is mainly for voice transmission, high-speed and broadband will gradually be required.
A method of increasing a transmission capacity includes a Time Division Multiplexing (TDM) method and a Wavelength Division Multiplexing (WDM) method.
The OTH has a minimum bit-rate??? unit of 2.5 G, and the TDM method hierarchy is standardized with a quadruple interval up to 10G and 40G.
Although increasing speed per channel by using the above-described method may easily increase transmission speed, the method is disadvantageous for chromatic dispersion, Polarization Mode Dispersion (PMD), and non-linearity in an optical fiber.
Thus, a more common method of increasing an entire capacity is a method of combining a plurality of data per channel at a relatively low speed by using the WDM method.
A problem with this method is that the OTN receives a tributary signal including not only OTH signals but also signals from various types of networks. Also, in the case of the SDH 40 G are standardized, and therefore a 40 G signal should be received as a tributary signal from the beginning.
Thus, if all 40 G signals are transmitted through one channel, various additional compensating devices are required because of the above-described problem where the 40 G signal has to be received as a tributary signal from the beginning, so that the cost for the entire system will be increased and a system will become complicated.
On the other hand, in the OTH, a Virtual Concatenation (VC) method is standardized.
The VC method reduces wasting of frames even when receiving various tributary signals since an interval between transmission frames is increased by quadruple intervals in the OTH.
For example, when receiving 5 channels of a giga-bit Ethernet signal as tributary signals, 10 G (Optical channel Data Unit (ODU) 2/Optical channel Transport Unit (OTU) 2) has to be selected while 5 G frames are wasted since there is no additional hierarchy between 2.5 G (ODU1/OTU1) and 10 G (ODU2/OTU2) in the OTH.
A number (a natural number) of frames at low speed can be combined by using the VC method, and therefore it is possible to receive 5 G frames (ODU1-2v) by combining 2 2.5 G frames. In this case, almost no frame is wasted during the transmission.
When transmitting by using the VC method, data is loaded into 2 different frames and transmitted individually through each network, and therefore a time delay between the frames will occur.
Thus, when receiving the above-described frames, the frames should be re-transformed to an original signal, which requires a rearrangement procedure by compensating for the difference of the time delay of each virtual concatenated signal frame.
Also, transmitting such a high speed signal causes problems in optical fiber transmission and electric signal transmission.
As the speed of the signal becomes higher, loss and distortion of a signal increase according to a distance in a medium having the same permittivity. In order to solve the loss and distortion problems, a method of transmitting signals by dividing signals into parallel signals is used.
However, although it is very easy to serialize signals when receiving the signals if the original signal is multiplexed at a low speed, a problem occurs when making frames which were originally at a high speed be in parallel.
For example, when transmitting 40 G signals to 2.5 G 16 channels by making them be in parallel, if the 40 G signals are signals to which original 2.5 G 16 channel signals are multiplexed according to the OTH multiplexing method, the signals can be transmitted to the receiving end by demultiplexing the signals into 16 channels, and the 16 channels can be received in each receiving end again and multiplexed to 40 G.
However, if the 40 G signal is one data frame such as a SDH Synchronous Transport Module (STM)-256 signal from the beginning, a problem occurs when making the signal into 16 parallel channels. In this case, frequency time delays occur in each of the 16 channels as it occurred in the transmission from the optical fiber, and therefore differences in the time delay should be compensated for when receiving the signal, in order to multiplex the channels into one signal again.
Research into an optical Printed Circuit Board (PCB) is in progress as one of the methods of transmitting high-speed electric signal.
In the case of an electric signal pattern, products having a back plane up to 2.5 G are currently on the market.
However, in order to increase capacity, each electric pattern should be verified against a 10 G series signal that is a next hierarchy (of 2.5 G???).
Also, another method of increasing the capacity includes a method of increasing a number of 2.5 G ports, but a problem occurs in that a back plane layout becomes complicated. In particular, when a standard is already determined, for example, a number of ports have been already determined in an Advanced Telecom Computing Architecture (ATCA), the method of increasing the number of ports for increasing capacity can be used.
Therefore, in order to solve the above-described problems, a back plane may be designed by using an optical PCB method which uses an optical line having barely any power loss compared to the electric pattern. However, the electric-optical conversion and optical-electric conversion should be performed in the optical PCB. Also, it is difficult to obtain reliable formation up to 10 G because of a difficulty in employing the optical line in the PCB.